something that works like a filter, as by removing, blocking, or separating out certain elements: Kids often talk without a filter. Events can be distorted through the filter of memory.

Informal. a filter-tipped cigarette or cigar.

Photography. a lens screen of dyed gelatin or glass for controlling the rendering of color or for diminishing the intensity of light.

Electronics, Physics. a circuit or device that passes certain frequencies and blocks others.

Mathematics. a collection of subsets of a topological space, having the properties that the intersection of two subsets in the collection is a subset in the collection and that any set containing a subset in the collection is in the collection.

verb (used with object)

to remove by the action of a filter.

to act as a filter for; to slow or partially obstruct the passage of: The thick leaves filtered the sunlight.

to pass through or as through a filter.

verb (used without object)

to pass or slip through slowly, as through an obstruction or a filter: Enemy agents managed to filter into the embattled country.

filter

filter

n.

early 15c., from Old French filtre and directly from Medieval Latin filtrum "felt," which was used to strain impurities from liquid, from West Germanic *filtiz (see felt (n.)). Of cigarettes, from 1908.

filter

[fĭl′tər]

A material that has very tiny holes and is used to separate out solid particles contained in a liquid or gas that is passed through it.

A device that allows signals with certain properties, such as signals lying in a certain frequency range, to pass while blocking the passage of others. For example, filters on photographic lenses allow only certain frequencies of light to enter the camera, while polarizing filters allow only light polarized along a given plane to pass. Radio tuners are filters that allow frequencies of only a narrow range to pass into an amplification circuit.